1. Field of the Invention
The present invention relates to a low-temperature chip bonding technology, and in particular relates to a eutectic solder structure for a chip that can bond chip at a relatively low temperature.
2. Description of the Related Art
The metal eutectic bonding process is a widely used bonding technology which can be involved in three-dimensional integrated circuit (3DIC) technology and can be utilized in the packaging processes of electronic devices such as light-emitting diodes (LEDs), laser diodes (LDs), or micro-electro-mechanical systems (MEMS). Due to features such as the structure of metal atoms being closely packed and the eutectic temperature of multicomponent metal system being lower than the melting point of pure metal, the bonding process can be carried out at a relatively low temperature. Accordingly, the negative effects brought about by the high-temperature process can be avoided.
Conventionally, when a chip is bonded onto a substrate through a metal eutectic bonding process, continuous metal layers having different melting points are alternately laminated on a bonding substrate to form a solder structure. Then, a heat treatment is performed to facilitate the reaction of the solder structure for forming intermetallic compounds such that a stable bonding can be achieved. However, when the process temperature is greater than or approximate to the melting point of the metal layer having a relatively low melting point, the fluidity of the metal layer having the relatively low melting point will increase. As a result, the metal layer having the relatively low melting point may flow to the outside of the solder structure, and voids may be formed in the solder structure or the solder structure may collapse. Accordingly, it is hard to obtain good bonding interface properties.
Though the existing eutectic solder structure has been used in various applications, a eutectic solder structure that can solve the above problems is still under requirement.